1. Field
The present disclosure relates generally to aircraft and, in particular, to a method and apparatus for refueling aircraft. Still more particularly, the present disclosure relates to a method and apparatus for controlling the refueling of aircraft and increasing the rate at which refueling may be accomplished.
2. Background
Commercial aircraft and military aircraft may be refueled in between flights on ground, while at airport terminals, and/or at other locations within an airport or airfield. These aircraft are refueled by a fuel delivery system such as, for example, without limitation, an airport hydrant system, a tanker truck, and/or some other type of fuel delivery system. In addition, aircraft are also refueled in flight by aerial refueling tankers. These fuel delivery systems send fuel into fuel tanks in an aircraft through an aircraft refueling system. An aircraft refueling system includes a refueling manifold that distributes fuel to the fuel tanks. The refueling manifold is typically located within the wing structure of an aircraft. In some cases, the refueling manifold may extend to fuel tanks located within the fuselage and/or in the tail of the aircraft. The refueling manifold may have a number of branches that extend from the refueling manifold to a number of individual fuel tanks.
The aircraft fuel tanks may also include a fuel vent system, also referred to as a vent system. This vent system regulates pressure within the fuel tanks. During overfill conditions, fuel, gas, and/or vapors may pass through the fuel vent system to an overfill tank and/or overboard from the aircraft. The overfill tank is a tank where fuel overfill may flow before exiting an aircraft.
Currently, refueling of larger commercial and/or military aircraft can take longer intervals of time than desired. For example, a large air transport aircraft can hold up to around 50,000 gallons of fuel to around 60,000 gallons of fuel. Refueling of this aircraft can take over around an hour at lower refueling pressures even at several hundreds of gallons per minute.
Longer refueling times may cause aircraft to occupy airport terminals for longer durations. Longer refueling times may also cause longer turnaround times of aircraft and increased delays at airports. Further, longer turnaround times and increased delays may increase airport congestion. This airport congestion can increase carbon emissions at an airport and decrease airport safety.
Further, with aerial refueling, longer refueling times lead to longer intervals of time of physical contact between a receiver aircraft and a refueling boom on an aerial refueling tanker. The longer intervals of time of physical contact between the aerial refueling tanker and the receiver aircraft may increase the risk to both aircraft.
Factors that influence refueling times include refueling quantity, refueling rates, and the amount of fuel remaining from a previous flight or in reserve. The upper limits of aircraft refueling rates may depend on protection of the limits of tank bottom pressure during an overfill condition. Protection of the limits of tank bottom pressure, in turn, is dependent on the venting capacity of the vent system to flow fuel. The upper limits of aircraft refueling rates may also depend on the limiting of flow velocities of fuel entering the refueling tanks. For example, limiting flow velocities may limit or prevent electrostatic charge.
Tank bottom pressure is the pressure that is present at the bottom of a fuel tank in the aircraft. The tank bottom pressure limit is the structural limit selected for the fuel tank or wing structure of an aircraft to avoid undesired changes to the structure of the fuel tank or elsewhere in the wing. The tank bottom pressure is highest during an overfill condition due to fuel static head pressure and back pressure. The back pressure is due to fuel flow losses through the vent system as fuel flows to an overfill tank and/or overboard. Tank bottom pressure limits are protected by limiting the refueling rate for each fuel tank to a rate that can flow through the vent system and overboard without producing an undesired increase in back pressure in the tank.
Therefore, it would be advantageous to have a method and apparatus for refueling an aircraft that takes into account one or more of the issues discussed above, as well as possibly other issues.